The present invention relates to gas discharge light-producing systems and methods and, more particularly, to low-current, non-thermionic (e.g., no heated filament) ballast-free energy-efficient light-producing systems and methods which are more efficient, less expensive, substantially free of RF emissions and which can use conventional industrial, commercial or home gas discharge lamps (fluorescent tubes of various shapes and sizes, high-intensity discharge lamps, sodium vapor lamps, mercury vapor lamps, neon signage tubes).
In most commercial and home-grade fluorescent lighting systems, the heart of the system is the ballast, which is an inductance or transformer device that boosts the incoming voltage to a higher voltage level to start the fluorescent tubes and then, once the fluorescent tubes are lit or ignited (gas ionized or discharged), reduces the voltage to a level for normal continuous lighting.
Moreover, these prior systems often use transformer filament windings to heat the filaments to therefore provide thermionic emission for assisting in the ignition phase. Heated filaments vaporize and form black deposits at the end of each tube and limit tube life. The evaporation of the Tungsten filament invades the mercury Vapor limiting luminosity and tube life. Early ballasted fluorescent lighting systems are shown in FIGS. 1A and 1B. In FIG. 1A the ballast unit L is in series with filaments F and switch S, and in FIG. 1B, glow switch GS which opens after the filaments are heated to initiate a discharge.
Ballast transformers are often the most expensive part of commercial fluorescent lighting systems. There have been numerous past efforts to provide fluorescent lighting systems which do not use ballast transformers.
Electronic ballasts of the type shown in FIG. 1C are common in the art and are disclosed in International Rectifier Publication Application Notes AN-995, xe2x80x9cElectronic Ballasts Using the Cost-Saving IR2155 Driverxe2x80x9d. In this circuit, two power switches Q1, Q2 are connected in a totem pole topology with the tube circuits consisting of an LC series resonant circuit with the lamp across one of the reactances. The switches are power MOSFETS driven to conduct alternately by windings on current transformer T. In this circuit, the primary winding is driven by current to the lamp circuit and operates at the resonant frequency of L and C. A starting pulse is provided by a starting circuit comprised of resistor R1 and capacitor C1 and DIAC D1 connected to one of the gates of one of the power switches. After oscillation is initiated, a high frequency square wave (30-80 kHz) excites the LC resonant circuit. The sinusoidal voltage across the reactance C is magnified by the Q at resonance and develops sufficient amplitude to strike the fluorescent lamp. In this system, the filaments of the lamp are connected in series with the series resonant circuit.
In the case of neon tubes as used in neon signage, conventional art uses high voltage (as a rule of thumb approximately 1000 volts per foot of sign) ballasted driver circuits which are inefficient, noisy, large, emit heat, require heavy high voltage insulation, are not usually dimmable).
The basic objective of the present invention is to provide improved gas discharge light-producing systems and methods.
Another object of the present invention is to provide a more energy-efficient gas discharge light-producing system and method.
Another object of the invention is to provide a more energy-efficient light-producing system which is low in cost and operates at and low currents.
Another object of the invention is to provide a light-producing system having a square wave voltage in the frequency range of about 75 kHz to about 3.5-4 MHz.
Another objective of this invention is to provide a light-producing system wherein one or more conventional gas discharge tubes is non-thermionically operated and driven by a high-frequency alternating current square wave source.
Another objective of this invention is to provide a gas discharge lighting system wherein multiple gas discharge tubes are electrically connected in series and non-thermionically driven by a square wave voltage.
Another object of the invention is to provide a gas discharge light-producing system in which the light intensity is variable from low-level illumination to high-level illumination and from high-level illumination to low-level illumination.
According to the invention, non-thermionic, ballast-free, fluorescent lighting system comprises at least one gas discharge light-producing lamp or tube and an alternating current square wave power supply. The square wave power supply incorporates a solid state switch means which is operated to generate a substantially square wave alternating current wave at the lamp or tube electrodes such that the voltage supplied to the electrodes reverses polarity more rapidly than the pattern of electron and ion density in the tube can shift so that electrons throughout the length of the device are continually accelerated and will, through several cycles of the applied square wave, create free electrons and ions throughout the tube""s volume, in steady state operation and ionize the gas lighting lamp.
According to a preferred embodiment of the present invention, at least one light-producing device with electrodes (which may be conventional filaments or not) immersed in a gaseous discharge medium (such as noble gases, argon, neon, helium or xenon, and mercury vapor and mixtures thereof; however, other gases and gas mixtures can be used) and is non-thermionically (no heater or filament currents) driven with a high-frequency square wave voltage. In the preferred embodiment, the driver circuit includes an inverter circuit using two solid state switching devices which are connected in totem pole fashion across a direct current supply. The gate electrode of each switch transistor is connected in circuit with a primary winding for each switch device and a primary winding of the transformer. A starting circuit to start the oscillator is utilized to provide a positive turn-on pulse to the gate electrode of one of the transistor switches. When one of the transistor switches turns on, its voltage is rapidly switched to ground which starts the circuit in oscillation. In the preferred embodiment, the oscillating frequency is set at about 100 kHz, but the range of successful operation runs from about 75 kHz through about 4 MHz. Since there are no high voltages in the driver circuit, safe operation is assured.
Illumination or luminosity levels or dimming can be achieved by varying the voltage (or energy level) from the direct current supply. In the preferred embodiment, care is taken to assure that there are no spike voltages due to inductive kick and the like. Since the gas discharge lamps or devices are non-thermionically driven, the luminous efficiency is significantly improved. Moreover, at the preferred high frequency of 100 kHz, power supply components can be smaller.
A salient difference between the system of the present invention and traditional fluorescent lamp systems is the marked reduction of heat that accompanies a given light output, which is in turn the reason why their efficiency of conversion of electricity to light is so high. Some of the heat reduction is, of course, recognizable as resulting from the absence of direct heating of the filaments in each end of the tube by applied voltages. Some is also explained in terms of energy transfer in the high-field region which occurs near the momentary cathode. However, fluorescent and neon tubes in the system of the present invention are much cooler throughout their length, including areas that are at great distances from the filaments whose heating could not possibly be explained by conduction, radiation, or diffusive heat transfer through the low-pressure gas filling the tube. (The overall applied voltage is not large enough to suggest that local regions of high field exit in tubes driven by the present invention.)
Cooling along the length of the tube is believed to be explainable in terms of energy transferred to electrons and ions by the applied electric field. In the present invention, the square wave voltage applied to the tube reverses so frequently that positive ions in the discharge can build up little kinetic energy during a half-cycle of the applied voltage. In conventional systems, larger amounts of energy can be acquired by ions in one-half cycle. This kinetic energy contributes nothing to light output, but in conventional systems is rapidly transferred to the neutral gas molecules and thence to the walls of the tube.
A major source of energy loss in conventional fluorescent tubes is caused by need to almost completely reconstitute ionization in the tube, at the beginning of each half-cycle. This requires not only energy to ionize electrically neutral gas molecules, but additional energy representing losses when electrons collide with neutral gas molecules and thereby increase their motional energy without ionizing the molecules. The non-thermionic, ballast-free system of this invention also works on other gases different from mercury vapor, like neon, neon/helium, sodium vapor, neon/argon and others as well as plasma displays.
The fact that the system is non-thermionic and ballast-free eliminates the danger and cause of electrical fires caused by overheated ballast driven systems.
The invention has the following further features:
(1) Being non-thermionic, you can intermingle gas discharge devices of different ratings, like the new xe2x80x9cwatt miserxe2x80x9d 32 watt or the new 25 watts xe2x80x9cenergy saversxe2x80x9d with the xe2x80x9cstandardxe2x80x9d 40 watts (four footers). The light output essentially remains the same regardless of the tube rating. Today""s usual shop lights can only use 40 watt regular tubes due to the shortcomings of the ballast as well as the use of chains to hang them because they can be a fire hazard. In order to demonstrate the efficacy of the system, a four-foot fluorescent tube (Sylvania rapid start F40) with blackened end (indicative of a non-working filament) was connected in series with a two-foot length of conventional neon signage tubing and both were successfully driven according to the principles of the present invention. Single pin (slimline) and reduced mercury content (Alto) fluorescent tubes are also included.
(2) Being ballast-free, the fixture weight and operating temperature are substantially reduced, eliminating the need for chain hanging. The system is not a temperature driven fire hazard.
(3) Since the system is ballast-free, there is no need for a sound rating because the system is silent. The greatly reduced heat and weight will allow the use of a plastic housing, eliminating the xe2x80x9celectric shock hazardxe2x80x9d as well as the need for grounding, necessary for the ballast to perform. Tubes in general should not be more than 1xe2x80x3 from a grounded surface.
(4) Being of reduced heat, the system can be mounted in any orientation and in contact with standard combustible surfaces (wood, wallpaper, etc.).
(5) The tubes, if filamented, will keep emitting normal light even in the event that one or both filaments are inoperative or open-circuited.
(6) Most fluorescent arrays or multiple tube units consist of identical tubes in parallel. The plural or multiple tube array systems can comprise identical or different rated tubes in series.
(7) Standard {fraction (11/4)} and {fraction (11/2)} inch diameter four-feet long fluorescent tubes filled with conventional mercury vapor or reduced mercury fluorescent tubes and/or argon gases, T5 1xe2x80x3 diameter (slimline) single pin fluorescent tubes and simple non-filamentary electrodes, and even conventional tubes with non-working or burned out filaments have been successfully used in the practice of this invention. One of the features of the invention is the use of conventional fluorescent tubes with non-working filaments, or blackened ends can be rehabilitated using the invention disclosed herein.
(8) Flexible plastic tubing, such as used in surgical gas transport systems, with or without UV responsive phosphors incorporated on the walls therein, Lexan(trademark) type hard plastic, shatter-proof gas retention vessels with simple discharge electrodes in the gas, with or without fluorescent coatings on the walls or fluorescent materials incorporated in the plastic, or rigid plastic tubes, on flexible tubing (the fluorescent mixture is preferred to be mixed with the tubing material) can be driven in accordance with the invention. In such cases, the darkening of the plastic due to UV bombardment with time can be advantageous, or the darkening can be prevented with a UV transparent blocking coating.
(9) Flexible plastic tubing and non-glass, plastic shatterproof neon signage with electrodes at the ends and filled with one of the discharge gases noted above (as in conventional neon signs, for example) have been successfully driven using the driver circuit principles and methods disclosed herein.